The expression of tyrosinase increases during oncogenesis and is commonly overexpressed in melanoma. Tyrosinase can oxidize various quinone compounds, such as dietary polyphenols, thereby activating or increasing their bioactivity. Quercetin (Qct) is a ubiquitous and abundant dietary polyphenol which exhibits antioxidant properties, but it can also form reactive quinone species after it is oxidized by enzymes such as tyrosinase. Activation of quercetin can lead to anti-tumorgenic events, such as the induction of phase II detoxification enzymes (NQO1 and GST), the stabilization of p53 and expression of its downstream targets (Bax, PUMA, p21 and GADD45). Preliminary data in melanoma cells which overexpress tyrosinase indicate that Qct exposure selectively activates ATM and subsequent p53 pathways, which have been shown to have anti-tumor properties. We also demonstrate that Qct negatively regulates Np73, a p53 antagonist. The overall goal of this proposal is to demonstrate that tyrosinase can be utilized as a molecular target of quercetin and prevent cancer. The aims of this proposal will test the overall hypothesis that dietary quercetin will reduce the tumor incidence or tumorigenicity of tyrosinase-positive cells. Specific Aim 1 will investigate the mechanisms of Qct-induced chemoprevention in vitro in normal melanocytes and melanoma cells using a three-dimensional human epidermal model. Specific Aim 2 will investigate the effect of dietary Qct on the reduction of tumor incidence in vivo using melanoma cells that overexpress tyrosinase in animals given a diet containing Qct. Aim 2 will also explore the use Qct adducts as a biomarker for measuring Qct activation and effectiveness. The aims of the proposed project are in alignment with the program announcement for Exploratory Cancer Prevention Studies Involving Molecular Targets for Bioactive Food Components. It addresses the initiative to promote research focused on the identification and characterization of molecular targets for bioactive food components. Results will provide a mechanistic basis and rationale for consumption of specific whole foods or supplementation to prevent cancer. PUBLIC HEALTH RELEVANCE: Melanoma is one of the fastest growing cancers and it is now estimated that one out of every 55 men or 82 women in the U.S. will be diagnosed with melanoma within their lifetimes. Current chemotherapies used for the treatment of melanoma are relatively ineffective, therefore this project focuses on the prevention of melanoma by selectively targeting tyrosinase, a protein that is highly expressed in melanoma tumors and during melanoma development. This project explores the potential of tyrosinase to selectively activate and increase the effectiveness of quercetin, an abundant dietary component with anti-cancer properties, and its role in the prevention of melanoma.